The relay of the invention may be used, for example, in defribrillator systems, in which double-throw, double-pole relays are used selectively to introduce a high voltage to the heart of the patient under precisely controlled conditions.
The relay is required to operate at high voltages, so that vacuum relays are well suited for the purpose because their contacts are enclosed within an evacuated envelope, and contact deterioration is materially reduced. However, ionization effects in vacuum relays has substantially limited their usefulness in that area.
The prior art relays of the type under consideration incorporate an envelope filled with a pressurized dielectric gas, such as sulfur hexafluoride (SF.sub.6) to reduce the ionization within the envelope, and also to provide a cooling effect. Mixtures of sulfur hexafluoride with argon and nitrous oxide have also been used to provide an effective gaseous atmosphere within the relay to prevent ionization effects and to provide the desired cooling. Activated alumina may be introduced into the housing as a getter for the corrosive fluorine compounds, in order to prevent harmful effects should the sulfur hexafluoride break down.
Problems have been encountered in providing suitable insulating rods on which to mount the movable contacts in such prior art gas-filled relays. This is because the rods must exhibit high insulating characteristics, high strength, and yet be immune to corrosive attacks from the gas or gases within the envelope. The prior art relays exclusively have used sapphire rods since, prior to the present invention, sapphire rods were considered to be the only rods which fulfilled all the criteria. However, sapphire rods are extremely expensive, and are somewhat brittle.
In the relay of the present invention, the sapphire rod of the prior art is replaced with a rod formed of a glass filled epoxy resin. This latter rod is inexpensive, and yet it possesses all the strength and electrical insulating properties of the prior art sapphire rods. In addition, the glass filled epoxy rod exhibits a resiliency which is most advantageous in assuring that firm electrical contact between the movable and fixed contacts of the relay will be maintained over long operating periods and under changing ambient conditions.
In the practice of the invention, glass filled epoxy resin rods are purchased as a standard item, and are then centerless ground to the desired diameter, and cut to the desired length.